JP6672886B2 - Loop antenna and wireless tag - Google Patents

Description

  The present invention relates to, for example, a loop antenna and a wireless tag having the loop antenna.

  Conventionally, a Radio Frequency Identification (RFID) system has been used for various purposes such as product management. Wireless tags used in RFID systems can be attached to various objects. Therefore, an antenna suitable for mounting on a wireless tag that can exhibit stable performance regardless of an article to which the wireless tag is attached has been proposed (for example, see Patent Documents 1 and 2).

  For example, Patent Literature 1 discloses a loop antenna formed by a first conductor and a second conductor. In this loop antenna, the first conductor forms a first curved surface, has a third terminal connected to a first terminal of the wireless communication circuit at a first end in the first curved surface, and has a first curved surface. A second region opposite the first end has a first region. The second conductor forms a second curved surface, has a fourth terminal connected to a second terminal of the wireless communication circuit at a third end in the second curved surface, and has a third end in the second curved surface. A second region at a fourth end opposite the portion. The first region and the second region overlap each other in parallel, and the first curved surface and the second curved surface form a loop antenna.

  Patent Document 2 discloses a line in the case of a reciprocating about 1 wavelength line with an electrical length of about 1/2 wavelength line and a strip or linear parallel line antenna in which a reciprocating about half wavelength line with about 1/4 wavelength. Have been. In this linear parallel line antenna, even if the antenna is mounted on a metal surface, the width of the metal body on the metal body on the lower surface opposite to the metal body on the radiation surface side to which the feeder or IC is attached is slightly increased. A change in the electric field of the line is prevented from occurring.

JP 2011-109552 A JP 2014-127752 A

  Depending on the article to which the wireless tag is attached, it is required that the size of the antenna mounted on the wireless tag be further reduced. However, as the size of the antenna decreases, the sensitivity of the frequency characteristics of the antenna to variations in the size of each part of the antenna due to manufacturing errors increases.

  Therefore, an object of the present specification is to provide a loop antenna capable of suppressing a change in frequency characteristics due to a manufacturing error.

  According to one embodiment, a loop antenna is provided. The loop antenna has a first pattern having conductivity and provided along a first surface and having a first feeding point, and a first pattern at a first end of the first surface. A first conductor having a second pattern connected to the pattern and provided to face the first pattern; and a first conductor having conductivity and having a first surface on the first surface. A third pattern having a second feeding point and a third pattern provided at a second end of the first surface opposed to the first end, the third pattern being provided with a gap between them to generate capacitance therebetween; And a second conductor having a fourth pattern that overlaps with the second pattern so as to be electrostatically coupled to the second pattern or that is connected to the second pattern. Then, at least a part of the first pattern is located closer to the second end than at least a part of the third pattern, and a current path from the first feeding point to the second feeding point is formed. A first feeding point and a second feeding point are provided so as to include at least a part of the first pattern.

  According to yet another embodiment, a wireless tag is provided. This wireless tag is connected to a loop antenna having a first feeding point and a second feeding point, and connected to the loop antenna by a feeding line that feeds the first feeding point and the second feeding point. And a communication processing circuit for emitting or receiving a wireless signal. The loop antenna has a first pattern that is conductive and is provided along the first surface and has a first feeding point, and a first pattern at a first end of the first surface. Between the first conductor having the second pattern connected to the first pattern and the second pattern provided so as to face the first pattern, and having a conductivity and having the first surface on the first surface. And a third pattern having a second feeding point and a third pattern at a second end of the first surface facing the first end. And a second conductor having a fourth pattern that is connected to and overlaps the second pattern so as to be capacitively coupled to the second pattern. Then, at least a part of the first pattern is located closer to the second end than at least a part of the third pattern, and a current path from the first feeding point to the second feeding point is formed. A first feeding point and a second feeding point are provided so as to include at least a part of the first pattern.

The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed.

  The loop antenna disclosed in this specification can suppress a change in frequency characteristics due to a manufacturing error.

It is an equivalent circuit diagram of a loop antenna and a communication circuit. (A) is a schematic perspective view of the loop antenna according to the first embodiment, and (b) is a schematic side view of the loop antenna according to the first embodiment. FIG. 3 is an exploded view of parts of the loop antenna shown in FIGS. 2 (a) and 2 (b). FIGS. 4A to 4C are diagrams illustrating dimensions of respective units used for an electromagnetic field simulation of the frequency characteristics of the loop antenna according to the first embodiment. FIGS. FIG. 6 is a diagram illustrating a relationship between a frequency and a communicable distance of the loop antenna according to the first embodiment, obtained by an electromagnetic field simulation. (A) And (b) is a figure which shows the dimension of each part used for the electromagnetic field simulation of the frequency characteristic of the loop antenna by a comparative example, respectively. FIG. 9 is a diagram illustrating a relationship between a frequency and a communicable distance of a loop antenna according to a comparative example, obtained by an electromagnetic field simulation. It is the schematic perspective view which looked at the loop antenna by 2nd Embodiment from the surface side. (A) and (b) show the loop antennas according to the third and fourth embodiments, respectively, in which the surface pattern of each conductor is formed so that the gap between the two conductors has a meandering shape, as viewed from the front side. FIG. It is the schematic perspective view which looked at the loop antenna by 5th Embodiment from the surface side in which each conductor was formed so that the front-end | tip part of each conductor might become U shape. FIG. 11 is a schematic perspective view of a loop antenna according to a sixth embodiment in which a protrusion is formed at a tip end in the loop antenna illustrated in FIG. 10, as viewed from a front surface side. FIG. 11 is a schematic perspective view of a loop antenna according to a seventh embodiment in which each conductor is formed such that two folded end portions of the loop antenna shown in FIG. . In the loop antenna shown in FIG. 10, the conductor shape of the loop antenna according to the eighth embodiment in which each conductor is formed such that the shape of the back pattern of each conductor is substantially equal to the shape of the surface pattern of each conductor FIG. It is a schematic perspective view of a loop antenna by a 9th embodiment in which each conductor was formed so that a gap between two conductors may extend along a diagonal direction of a substrate. FIGS. 9A and 9B are diagrams illustrating examples of changes in the width of each conductor and the width of a gap due to a manufacturing error in the loop antenna illustrated in FIGS. For reference, an electromagnetic field showing an example of the relationship between the manufacturing error and the resonance frequency f0 for the loop antenna shown in FIG. 8 when the fluctuation of the resonance frequency f0 due to the fluctuation of the inductance _Lap due to the manufacturing error is insufficient. It is a figure showing a simulation result. Electromagnetic field simulation results showing an example of the relationship between the manufacturing error and the resonance frequency f0 for the loop antenna shown in FIG. 8 when the change in the resonance frequency f0 due to the change in the inductance _Lap due to the manufacturing error is appropriately suppressed. FIG. FIG. 11 is a diagram showing dimensions of each part of the loop antenna shown in FIG. 10 designed so as to appropriately suppress a change in the resonance frequency f0 due to a change in the inductance L _ap due to a manufacturing error. In the case where designed to be adequately suppress variations in the resonance frequency f0 due to the variation of the inductance L _ap due to manufacturing errors, electromagnetic showing an example of a manufacturing error and the relationship of the resonance frequency f0 of the loop antenna shown in Fig 10 It is a figure showing a field simulation result. FIG. 9 is a schematic side view near the integrated circuit in the loop antenna illustrated in FIG. 8. It is a block diagram of the wireless tag which has a loop antenna by any of the above-mentioned each embodiment or its modification.

  Hereinafter, the loop antenna will be described with reference to the drawings. First, in order to clarify the factors that contribute to the frequency characteristics of the loop antenna, an equivalent circuit of the loop antenna and a communication circuit that performs communication using the loop antenna will be described.

FIG. 1 is an equivalent circuit diagram of the loop antenna and the communication circuit. The loop antenna is represented by an equivalent circuit 100 in which a resistance (resistance value R _ap ), a coil (inductance L _ap ), and a capacitor (capacitance C _int ) are connected in parallel. On the other hand, a communication circuit connected to the loop antenna is an equivalent circuit 101 in which a resistor (resistance value R _cp (for example, approximately 2000Ω)) and a capacitor (capacitance C _cp (for example, 1.0 pF)) are connected in parallel. It is represented by In a wireless tag, a loop antenna and a communication circuit may be connected without using a matching circuit. Therefore, it is required that the impedance of the equivalent circuit 100 and the impedance of the equivalent circuit 101 for a radio wave having a desired frequency match. That is, for a desired frequency, it is required that the loop antenna and the communication circuit satisfy the resonance condition. When the resonance condition is satisfied, the loop antenna can pass the received radio wave to the communication circuit. That is, the loop antenna can be used for radio waves in a frequency band having a predetermined width around the predetermined frequency. The resonance condition is represented by the following equation.

When the capacitances C _int and C _cp and the inductance L _ap satisfy the resonance condition at the resonance frequency f0, and R _ap = R _cp , all the power of the radio wave received by the loop antenna is supplied to the communication circuit. Is done.

In general, the resistance value R _cp and the capacitance C _cp of the communication circuit is fixed. Therefore, the capacitance C _int or the inductance L _ap is adjusted so that the resonance frequency f0 is a desired frequency, for example, such that the resonance frequency f0 is included in the frequency band 860 MHz to 960 MHz used in the RFID system. .

Here, the inductance _Lap of the coil of the equivalent circuit 100 increases as the length of the loop of the loop antenna, that is, the length of the path through which the current flows increases. The capacitance C _int is adjusted by, for example, the width of a gap between two conductors in an interdigital structure provided in a loop antenna. For example, the smaller the gap between two conductors in the interdigital structure, the larger the capacitance C _int . When the loop antenna does not have a structure that generates a capacitance such as an interdigital structure, the capacitance C _int becomes zero.

The size of the loop antenna may be limited due to the size reduction of the wireless tag on which the loop antenna is mounted. In such a case, it is difficult to increase the length of the loop of the loop antenna with the conventional technology, and thus it is difficult to increase the inductance _Lap . Therefore, in order for the resonance frequency f0 to be included in the frequency band allocated to the RFID system, the capacitance C _int must be increased, and as a result, the gap in the interdigital structure of the loop antenna is reduced. Will be.

However, as the gap becomes narrower, the ratio of the gap width variation due to the loop antenna manufacturing error to the gap width increases. Therefore, the fluctuation amount of the capacitance C _int due to the manufacturing error of the loop antenna also increases. As a result, the frequency characteristics of the loop antenna also fluctuate greatly due to manufacturing errors of the loop antenna. This is not preferable because the allowable tolerance applied when manufacturing the loop antenna must be reduced.

Therefore, in this loop antenna, by increasing the loop length of the loop antenna as much as possible within a limited size and increasing the inductance L _ap , the width of the gap of the interdigital structure that causes capacitance is made as wide as possible. . Therefore, in a loop antenna formed by surrounding a rectangular substrate with two conductors along its longitudinal direction, the feeding point of one conductor that is folded at one end of the substrate is connected to the other end of the substrate facing the one end. It is provided closer to the other end than the feeding point of the other conductor folded at the end. Thereby, this loop antenna can make the path of the current flowing through the loop antenna longer and increase the width of the gap formed between the two conductors.

  In the following embodiments or modified examples, for convenience of explanation, the surface of the substrate on which the power supply point is provided is referred to as the front surface, and the surface opposite to the substrate surface is referred to as the back surface. Also, the loop antenna is placed so that the longitudinal direction of the board is horizontal and the short side of the board is vertical, and the vertical and horizontal directions are based on the loop antenna viewed from the front side. Specify the direction. Further, the length of the substrate in the lateral direction may be referred to as the width of the substrate, and the length in the longitudinal direction of the substrate may be simply referred to as the length of the substrate.

  FIG. 2A is a schematic perspective view of the loop antenna according to the first embodiment, and FIG. 2B is a schematic side view of the loop antenna according to the first embodiment. FIG. 3 is an exploded view of parts of the loop antenna shown in FIGS. 2 (a) and 2 (b).

  The loop antenna 1 according to the first embodiment has a substrate 2, a first conductor 3, and a second conductor 4.

The substrate 2 is formed in a rectangular plate shape by a dielectric such as a synthetic resin such as an ABS resin, a PET resin, and a polycarbonate resin.
The first conductor 3 is, for example, a conductive metal such as copper or gold, and a plane is bent into a U-shape at one end (the right end in this example) in the longitudinal direction of the substrate 2. The shape has One side from the bent portion of the first conductor 3 forms a first surface pattern 3a provided on the surface of the substrate 2, and the other side from the bent portion is formed on the back surface of the substrate 2. A first back pattern 3b to be provided is formed. The first surface pattern 3a and the first back pattern 3b are electrically connected at the right end of the substrate 2.

  The first surface pattern 3a on the surface of the substrate 2 includes, in order from the right end side of the substrate 2, a rectangular first connection portion 3c and a rectangular first end portion 3d. The first connection portion 3c is provided from the vicinity of the right end of the substrate 2 to a position beyond a midpoint in the longitudinal direction of the substrate 2 by a predetermined offset, and the first connection portion 3c along the short direction of the substrate 2 Is less than 1/2 of the width of the substrate 2. The first tip 3d is provided between the left end of the first connection portion 3c and the other end (the left end in this example) of the substrate 2 in the longitudinal direction. The width of the first distal end portion 3d along the lateral direction of the substrate 2 is wider than 1/2 of the width of the substrate 2. The upper sides of the first connection portion 3c and the first tip portion 3d are parallel to the upper end of the substrate 2.

  On the other hand, the first back pattern 3b on the back of the substrate 2 is formed in a rectangular shape so as to cover the entire range from the right end of the substrate 2 to a position at a predetermined distance from the left end of the substrate 2.

  The second conductor 4 is also a conductive metal such as copper or gold, has a shape similar to that of the first conductor 3, and has a first shape with respect to the center of the surface of the substrate 2. The conductor 3 is formed so as to be symmetrical with the center point. That is, the second conductor 4 has a shape in which a plane is bent in a U-shape at the left end of the substrate 2. One side from the bent portion of the second conductor 4 forms a second surface pattern 4a provided on the surface of the substrate 2, and the other side from the bent portion is formed on the back surface of the substrate 2. A second back pattern 4b to be provided is formed.

  The second surface pattern 4a on the surface of the substrate 2 includes, in order from the left end side of the substrate 2, a rectangular second connection portion 4c and a rectangular second distal end portion 4d. The second connecting portion 4c is provided from the vicinity of the left end of the substrate 2 to a position beyond a midpoint in the longitudinal direction of the substrate 2 by a predetermined offset, and the second connecting portion 4c along the lateral direction of the substrate 2 Is less than 1/2 of the width of the substrate 2. The second tip 4d is provided between the right end of the second connecting portion 4c and the other end (the right end in this example) of the substrate 2 in the longitudinal direction. The width of the second distal end portion 4d along the short direction of the substrate 2 is larger than 1/2 of the width of the substrate 2. The lower side of the second connection part 4c and the second tip part 4d is parallel to the lower end of the substrate 2.

A gap 5-1 having a capacitance is formed between the first connection part 3c of the first conductor 3 and the second tip part 4d of the second conductor 4. Similarly, a gap 5-2 having a capacitance is formed between the second connecting portion 4c of the second conductor 4 and the first tip 3d of the first conductor 3. Thereby, the loop antenna 1 can set the capacitance C _int of the equivalent circuit of the loop antenna shown in FIG. 1 to a value larger than 0. The width of the gaps 5-1 and 5-2 is determined based on a frequency band in which the loop antenna 1 is used, an inductance corresponding to the electrical length of the loop antenna 1, and the like.

  Further, a protrusion 3e parallel to the second connection portion 4c is provided on a side of the first front end portion 3d facing the right end of the substrate 2, and a gap between the protrusion 3e and the second connection portion 4c is a gap. It is provided so as to be the same as 5-1. Similarly, a protrusion 4e parallel to the first connection portion 3c is provided on the side opposite to the left end of the second front end portion 4d, and the distance between the protrusion 4e and the first connection portion 3c is equal to the gap 5−. 2 is provided. Thereby, the loop antenna 1 can increase the gap between the first conductor 3 and the second conductor 4 and thus can increase the capacitance. In addition, since the projection 3e and the projection 4e have the tip 3d and the tip 4d extended, the loop antenna 1 can also increase the inductance.

  Furthermore, a portion between the side of the first end 3d of the first conductor 3 facing the right end of the substrate 2 and the side of the second end 4d of the second conductor 4 facing the left end of the substrate 2 In the space, for example, an integrated circuit 8 that executes various processes of the wireless tag such as a communication process is arranged. A first power supply point 6a on the negative electrode side is provided on the side of the first end 3d of the first conductor 3 facing the right end of the substrate 2. On the other hand, a second power supply point 6b on the positive electrode side is provided on a side of the second end 4d of the second conductor 4 facing the left end of the substrate 2. The feeding point 6a and the feeding point 6b are connected to the integrated circuit 8 via the feeding line 9, respectively.

As a result, the path through which the current flows from the feeding point 6a to the feeding point 6b includes the first connection part 3c and the second connection part 4c which cross each other. The length is longer than the length of one circumference of the substrate 2 along the longitudinal direction of the substrate 2. Therefore, the loop antenna 1 can increase the inductance _Lap in the equivalent circuit 100 of the loop antenna illustrated in FIG. 1 without significantly lowering the radiation characteristics.

On the other hand, on the back surface of the substrate 2, the second back pattern 4 b of the second conductor 4 is formed in a rectangular shape so as to cover the entire range from the left end of the substrate 2 to a position at a predetermined distance from the right end of the substrate 2. You. Therefore, on the back surface of the substrate 2, the first back pattern 3 b of the first conductor 3 and the second back pattern 4 b of the second conductor 4 have overlapping regions that overlap with each other. In the overlapping region, for example, a resin insulating film layer 7 is provided between the first back pattern 3b and the second back pattern 4b. Therefore, in the overlapping region, the loop antenna 1 has a capacitance, and the first conductor 3 and the second conductor 4 are electrostatically coupled in a frequency band in which the loop antenna 1 is used. Thereby, the capacitance C _int of the equivalent circuit of the loop antenna shown in FIG. 1 increases.

  The first conductor 3 is formed on the substrate 2 by, for example, vapor deposition. The second conductor 4 is provided on the substrate 2 by, for example, being deposited on the film layer 7 and then wound around the substrate 2 together with the film layer 7. Alternatively, the first conductor 3 and the second conductor 4 may be formed on the substrate 2 or the film layer 7 by various other methods of forming a conductor pattern on a dielectric substrate.

  Note that the loop antenna 1 may be housed in a case formed of a non-dielectric material.

Hereinafter, the frequency characteristics of the loop antenna 1 obtained by the electromagnetic field simulation will be described.
FIGS. 4A to 4C are diagrams illustrating dimensions of respective units used for an electromagnetic field simulation of the frequency characteristics of the loop antenna according to the first embodiment. 4A is a perspective view of the loop antenna 1 as viewed from the front side, and FIG. 4B is a perspective view of the case in which the loop antenna 1 is accommodated as viewed from the front side. FIG. 4C is a diagram illustrating a state where the first conductor 3 and the second conductor 4 are extended in a flat plate shape. In this simulation, the relative permittivity εr of the substrate 2 was set to 3.2 and the dielectric loss tangent tanδ of the substrate 2 was set to 0.001. The length of the substrate 2 was 31 mm, the width was 22 mm, and the thickness of the substrate 2 was 1.2 mm.

Further, the conductivity of the first conductor 3 and the second conductor 4 was set to 5.8 × 10 ⁷ (S / m). Then, the width of the first conductor 3 and the second conductor 4 along the lateral direction of the substrate 2 at portions other than the connection portion and the tip portion was set to 20 mm. On the other hand, the width of the first connection portion 3c and the second connection portion 4c along the short direction of the substrate 2 was 5.8 mm, and the length along the long direction of the substrate 2 was 17.5 mm. The width of the first tip 3d and the second tip 4d along the width direction of the substrate 2 was 13.2 mm, and the length of the substrate 2 along the longitudinal direction was 11.5 mm. Further, the width of the protrusions 3e and the protrusions 4e along the width direction of the substrate 2 was set to 0.7 mm, and the length of the protrusion 2 along the longitudinal direction was set to 4 mm. The distance between the first tip 3d and the second tip 4d along the longitudinal direction of the substrate 2 and the distance between the protrusion 3e and the protrusion 4e along the short direction of the substrate 2 are each 5 mm. And The width of the gap 5-1 and the width of the gap 5-2 were each set to 1 mm.

  Further, the lengths of the first back pattern 3b and the second back pattern 4b along the longitudinal direction of the substrate 2 were each set to 26 mm. That is, on the rear surface of the substrate 2, the first rear pattern 3b and the second rear pattern 4b overlap each other within a range of 21 mm along the longitudinal direction of the substrate 2 and 20 mm along the lateral direction of the substrate 2. The thickness of the film layer 7 was set to 0.1 mm, and the relative permittivity and the dielectric loss tangent of the film layer 7 were the same as the relative permittivity and the dielectric loss tangent of the substrate 2.

  Further, the width of the power supply line 9 connected to the first power supply point 6a and the second power supply point 6b was set to 0.26 mm. Further, a first feeding point 6a and a second feeding point 6b are provided at the midpoint in the lateral direction of the substrate 2.

  Further, in this simulation, the loop antenna 1 was housed in a dielectric case having the same relative dielectric constant and dielectric loss tangent as those of the substrate 2. The length of the case in the longitudinal direction was 35 mm, the length in the short direction was 25 mm, and the thickness was 2 mm.

  FIG. 5 is a diagram showing the relationship between the frequency and the communicable distance of the loop antenna 1 obtained by the electromagnetic field simulation. In FIG. 5, the horizontal axis represents frequency, and the vertical axis represents communicable distance. The graph 500 shows the relationship between the frequency of the loop antenna 1 having the dimensions of each part shown in FIG. 4 and the communicable distance. The graph 501 shows the gaps 5-1 and 5-2, the interval between the first tip 3d and the second tip 4d, and the interval between the two protrusions 3e and 4e, respectively, in FIG. 4C. 9 shows the relationship between the frequency of the loop antenna 1 and the communicable distance when the distance becomes 0.1 mm wider than that obtained. The graph 502 shows the gaps 5-1 and 5-2, the interval between the first tip 3d and the second tip 4d, and the interval between the two protrusions 3e and 4e, respectively, in FIG. 4C. FIG. 9 shows the relationship between the frequency of the loop antenna 1 and the communicable distance when the distance becomes smaller by 0.1 mm than that of the loop antenna.

  As shown in the graphs 500 to 502, in the loop antenna 1, the maximum communicable distance is almost constant even if the sizes of the gaps 5-1 and 5-2 change by ± 0.1 mm. Further, the frequency corresponding to the maximum communicable distance also varies only by ± 2.3 MHz. Thus, it can be seen that the loop antenna 1 has a small change in the frequency characteristic due to a manufacturing error in the dimensions of each part.

  FIGS. 6A and 6B are diagrams illustrating dimensions of respective parts used in an electromagnetic field simulation of the frequency characteristics of the loop antenna 600 according to the comparative example. FIG. 6A is a transparent perspective view of the case in which the loop antenna 600 is accommodated, as viewed from the front side. FIG. 6B is a diagram illustrating a state where two conductors forming the loop antenna 600 are extended in a flat plate shape. Also in this comparative example, a conductor is provided along the longitudinal direction of the substrate 601 having the same size and the same physical characteristics (relative permittivity εr = 3.2, dielectric loss tangent tanδ = 0.01) as the substrate 2 of the loop antenna 1 according to the first embodiment. Enclose the loop antenna 600. However, in this comparative example, capacitance is provided between the conductor 610 provided with the power supply point 602 on the positive electrode side and the conductor 611 provided with the power supply point 603 on the negative electrode side along the lateral direction of the substrate 601. Gap 612 is formed.

  In this comparative example, the width of the conductor 610 and the conductor 611 along the lateral direction of the substrate 601 was set to 20 mm. Then, a circuit for feeding the loop antenna 600 having a size of 4.78 mm along the longitudinal direction of the substrate 601 and 5 mm along the lateral direction of the substrate 601 is installed near the gap 612 on the conductor 610. Space 613 is formed. In the space 613, power is supplied to the power supply points 602 and 603 via a power supply line having a width of 0.2 mm. In order to separate the gap 612 from the space 613, two protrusions 614 and 615 are formed at the end of the conductor 610 on the gap 612 side along the lateral direction of the substrate 601. The width of the two projections 614 and 615 is 0.2 mm, and the distance between the tip of the projection 614 and the tip of the projection 615 is 0.208 mm. A power supply line for supplying power to the power supply point 603 is passed through this interval.

  Further, in order to maximize the communicable distance of the loop antenna 600 at the frequency at which the communicable distance of the loop antenna 1 becomes the maximum, the width of the gap 612 is set to 0.04 mm.

  Further, the lengths of the conductor 610 and the conductor 611 along the longitudinal direction of the substrate 601 for the portion located on the back side of the substrate 601 were each set to 26 mm. That is, on the rear surface of the substrate 601, the conductor 610 and the conductor 611 overlap each other within a range of 21 mm along the longitudinal direction of the substrate 601 and 20 mm along the lateral direction of the substrate 601. In a range where the conductor 610 and the conductor 611 overlap, the thickness of a film layer (not shown) provided between the conductor 610 and the conductor 611 is set to 0.1 mm. And the dielectric constant and the dielectric loss tangent are the same.

  Further, in this simulation, the loop antenna 600 is housed in a dielectric case having the same relative permittivity and dielectric loss tangent as the relative permittivity and dielectric loss tangent of the substrate 601. The length of the case in the longitudinal direction was 35 mm, the length in the short direction was 25 mm, and the thickness was 2 mm.

  FIG. 7 is a diagram illustrating the relationship between the frequency and the communicable distance of the loop antenna 600, obtained by the electromagnetic field simulation. In FIG. 7, the horizontal axis represents frequency, and the vertical axis represents communicable distance. The graph 700 shows the relationship between the frequency of the loop antenna 600 having the dimensions of each part shown in FIG. 6 and the communicable distance. Further, a graph 701 represents the relationship between the frequency of the loop antenna 600 and the communicable distance when the interval between the gaps 612 is 0.1 mm wider than that shown in FIG.

  As shown in the graphs 700 and 701, in the loop antenna 600, the maximum communicable distance is greatly reduced and the maximum communicable distance is equivalent to the maximum communicable distance only by changing the size of the gap 612 by 0.1 mm. The fluctuation range of the frequency is as large as 100 MHz or more. As described above, in the loop antenna 600, it can be seen that the change in the frequency characteristic due to the manufacturing variation of the dimensions of each part is much larger than that of the loop antenna 1.

As described above, in this loop antenna, along the longitudinal direction of the board, the tip of one of the two conductors formed so as to surround the board is connected to the tip of the other conductor. Two conductors are formed so as to cross each other, and power is supplied to each of the tips. That is, the feeding point of one conductor is provided closer to the end where the other conductor is folded than the feeding point of the other conductor. For this reason, in this loop antenna, the path of the current flowing between the two feeding points includes a leading end which is crossed, so that the path of the current flowing through the loop antenna becomes long. Therefore, the inductance L _{ap of the} loop antenna increases, and the required capacitance C _int is reduced. As a result, the loop antenna can increase the gap between the two conductors that generate the capacitance, so that the variation in the frequency characteristics due to the variation in the gap width or the like due to a manufacturing error can be suppressed.

  FIG. 8 is a schematic perspective view of the loop antenna according to the second embodiment as viewed from the front side. In FIG. 8, components corresponding to the components of the loop antenna 1 shown in FIGS. 2A and 2B are denoted by the same reference numerals. The loop antenna 11 according to the second embodiment is different from the loop antenna 1 according to the first embodiment in that the protrusions at the tips 3d and 4d of the conductors 3 and 4 are omitted. Therefore, in the loop antenna 11 according to the second embodiment, the length of the gaps 5-1 and 5-2 between the two conductors is shorter than the loop antenna 1 by the length corresponding to the protrusion. I have. Therefore, in order for the loop antenna 11 to have the same capacitance as the capacitance of the loop antenna 1 and the same inductance as the inductance of the loop antenna 1, for example, the gap 5-1 is smaller than that of the loop antenna 1. The width of 5-2 will be narrowed. Alternatively, in order to increase the inductance corresponding to the protruding portion, the distal end portions 3d, 4d are extended by the reduced width of the connecting portions 3c, 4c. However, in the loop antenna 11, since the fine protrusions are omitted, the manufacture is easier than in the loop antenna 1.

  According to another embodiment, the surface pattern of the two conductors may be formed such that the gap between the two conductors has a meandering shape.

  FIGS. 9A and 9B show loop antennas according to the third and fourth embodiments, respectively, in which the surface pattern of each conductor is formed such that the gap between the two conductors has a meandering shape. It is the schematic perspective view seen from the surface side. 9A and 9B, the components corresponding to the components of the loop antenna 11 shown in FIG. 8 are denoted by the same reference numerals.

  In the loop antenna 21 according to the third embodiment shown in FIG. 9A, the upper side of the first distal end portion 3d is different from the loop antenna 11 shown in FIG. The width of the first distal end portion 3d is narrower so as to be located closer to the center of the substrate 2 than the upper side of the portion 3c. The second conductor 4 extends to the right end side of the substrate 2 along the upper side of the first tip 3d. Similarly, the second end of the second conductor 4 is positioned such that the lower side of the second end 4 d is located closer to the center of the substrate 2 than the lower side of the second connection part 4 c. The width of the portion 4d is reduced. The first conductor 3 extends to the left end of the substrate 2 along the lower side of the second tip 4d. Therefore, the gap 5-1 and the gap 5-2 have a meandering shape, and the gap 5-1 and the gap 5-2 are longer than those of the loop antenna 11.

  Further, in the loop antenna 31 according to the fourth embodiment shown in FIG. 9B, not only the first tip 3d and the second tip 4d but also the upper side of the first connection 3c. A part and a part of the lower side of the second connection part 4c are also located closer to the center of the substrate 2 than the upper and lower ends of the substrate 2. Thereby, in the loop antenna 31, the length of the gaps 5-1 and 5-2 is further longer than that of the loop antenna 21.

  Thus, in the embodiment shown in FIGS. 9A and 9B, the gaps 5-1 and 5-2 between the two conductors are longer than the loop antennas according to the above embodiments. . Therefore, the loop antennas according to the third and fourth embodiments can further increase the width of the gap. As a result, the loop antennas according to the third and fourth embodiments can further reduce fluctuations in frequency characteristics due to manufacturing errors.

According to still another embodiment, the tip of each conductor may be formed in a U-shape.
FIG. 10 is a schematic perspective view of the loop antenna according to the fifth embodiment, as viewed from the front side, in which each conductor is formed such that the tip of each conductor is U-shaped. 10, the components corresponding to the components of the loop antenna 11 shown in FIG. 8 are denoted by the same reference numerals.

In the loop antenna 41 according to the fifth embodiment, the slit 3f extending from the side of the first distal end 3d facing the right end of the substrate 2 toward the left end of the substrate 2 is formed between the feed point 6a and the first end. And the connecting portion 3c. Therefore, the first distal end 3d is U-shaped. Similarly, a slit 4f extending from the side of the second front end portion 4d facing the left end of the substrate 2 toward the right end side of the substrate 2 is provided between the feeding point 6b and the second connection portion 4c. Is formed. Therefore, the second tip 4d is U-shaped. Therefore, in the loop antenna 41, as compared with the loop antenna according to each of the above-described embodiments, the path through which the current flows becomes longer and the width of the path through which the current flows becomes narrower at each end, so that the inductance L _ap is reduced. The required capacitance C _int can be further reduced. As a result, in the loop antenna 41, the width of the gaps 5-1 and 5-2 can be made wider, and the fluctuation of the frequency characteristic due to a manufacturing error can be further reduced. In addition, the loop antenna 41 can shift the resonance frequency f0 to a lower frequency side by increasing the length of the current flow path.

In addition, the extending direction of the slits 3f, 4f is not limited to the longitudinal direction, and the length of the path through which the current flows or the width of each conductor becomes narrow, that is, any direction that intersects the path of the current. It may be formed facing the direction. For example, the slit 3f may be formed upward from the vicinity of the boundary between the first distal end portion 3d and the first connection portion 3c shown in FIG. Similarly, the slit 4f may be formed downward from the vicinity of the boundary between the second tip 4d and the second connecting portion 4c. Also in this case, since the width of each conductor is reduced, the inductance _Lap is increased.

  Further, in order to reduce the width of each conductor in the current path and increase the inductance, a slit is formed in the second conductor 4 from one of the sides of the second conductor 4 facing the gap 5-1. May be done. For example, a slit may be formed in any part of the gap 5-1 parallel to the short direction (for example, above or below the slit 4f) so as to go to the left end. Similarly, a slit may be formed in the first conductor 3 from any side of the first conductor 3 facing the gap 5-2. For example, a slit may be formed in any part of the gap 5-2 parallel to the short direction (for example, above or below the slit 3f) so as to go to the right end. However, these slits do not have to be parallel to the longitudinal direction, and may be formed at an angle of, for example, 0 ° to 45 ° with respect to the longitudinal direction.

  Further, in order to reduce the width of each conductor in the current path and increase the inductance, a slit may be further formed downward from the upper end of the first connection portion 3c facing the gap 5-1. Similarly, a slit may be further formed upward from the lower end of the second connection portion 4c facing the gap 5-2. However, these slits may not be parallel to the short direction, and may be formed to form an angle of, for example, 0 ° to 45 ° with respect to the short direction. Further, a slit may be formed downward from the upper end of the first conductor 3 in a portion sandwiched between the gap 5-1 and the right end. Further, a slit may be formed upward from the lower end of the second conductor 4 in a portion sandwiched between the gap 5-2 and the left end.

  Further, the number of slits formed in the first conductor 3 is not limited to one, and may be plural. Similarly, the number of slits formed in the second conductor 4 is not limited to one, and may be plural. In this case, for example, for each of the first conductor 3 and the second conductor 4, any two or more of the slits may be formed. Further, each slit is not limited to a linear slit, and may be formed in an L shape, an arc shape, a meandering shape, or the like. Furthermore, only one of the first conductor 3 and the second conductor 4 may be provided with one or more of the slits.

  Further, in the loop antenna 41, in order to make the gaps 5-1 and 5-2 longer, protrusions extending along the longitudinal direction of the substrate may be formed at both ends of each tip.

  FIG. 11 is a schematic perspective view of the loop antenna according to the sixth embodiment, in which a protrusion is formed at the distal end, in the loop antenna 41 shown in FIG. 10, as viewed from the front side. 11, the components corresponding to the components of the loop antenna 41 shown in FIG. 10 are denoted by the same reference numerals.

  In the loop antenna 51 according to the sixth embodiment, two protrusions 3g, 3h extending from the upper end and the lower end of the tip of the first tip 3d to the right along the longitudinal direction of the substrate 2 respectively. Is formed. Similarly, two protrusions 4g and 4h extending leftward along the longitudinal direction of the substrate 2 are formed from the upper end and the lower end of the tip of the second tip 4d. As a result, in the loop antenna 51, the gaps 5-1 and 5-2 are longer than the loop antenna 41, and the distal ends 3d and 4d are also longer, so that the gap width can be further increased. As a result, the loop antenna 51 can further reduce fluctuations in frequency characteristics due to manufacturing errors. Alternatively, by setting the width of the gaps 5-1 and 5-2 equal to the width of the gaps 5-1 and 5-2 of the loop antenna 41, the resonance frequency f0 is shifted to a lower frequency side. In addition, each protrusion may be formed in a meandering shape, or the tip side may be extended along the lateral direction from the middle of the protrusion so as to be L-shaped.

  Further, in the loop antenna 41, each conductor may be formed such that the two folded end portions cross each other in order to make the current flow path longer.

  FIG. 12 is a front view of the loop antenna according to the seventh embodiment, in which each of the conductors is formed so that the two folded end portions of the loop antenna 41 shown in FIG. 10 cross each other. FIG. Further, the loop antenna according to the seventh embodiment shown in FIG. 12 includes the tip portions 3d and 4d of the conductors of the loop antenna shown in FIG. 2A or the conductors of the loop antenna shown in FIG. The projections 3e and 4e are extended to form a Rewound Spiral shape. 12, components corresponding to the components of the loop antenna 41 shown in FIG. 10 are denoted by the same reference numerals.

  In the loop antenna 61 according to the seventh embodiment, in the first surface pattern 3a of the first conductor 3 extending from the right end side of the substrate 2, the tip of the U-shaped first tip 3d is formed. , Is located closer to the right end of the substrate 2 than the tip of the second tip 4d. Conversely, in the second surface pattern 4a of the second conductor 4 extending from the left end side of the substrate 2, the tip of the U-shaped second tip 4d is the same as the first tip 3d. It is located closer to the left end of the substrate 2 than the tip. Therefore, the first distal end 3d and the second distal end 4d cross each other. The feeding points 6a and 6b are provided such that the direction connecting the feeding points 6a and 6b is substantially parallel to the short direction of the substrate 2.

  Further, the first surface pattern 3a is connected to the first back pattern at the lower end of the substrate 2. Similarly, the second surface pattern 4 a is connected to the second back pattern on the upper end side of the substrate 2. As a result, the path through which the current flows becomes longer.

In the loop antenna 61, the path through which the current flows is longer than in the loop antenna 41, so that the inductance L _ap is larger and the required capacitance C _int can be further reduced. Further, the gaps 5-1 and 5-2 also become longer. As a result, in the loop antenna 61, the width of the gaps 5-1 and 5-2 can be made wider, and the fluctuation of the frequency characteristic due to a manufacturing error can be further reduced. Further, the loop antenna 61 can shift the resonance frequency f0 to a lower frequency side as compared with the loop antenna 41.

  Further, in the loop antenna 41, each conductor may be formed such that the shape of the back pattern of each conductor is substantially equal to the shape of the surface pattern of each conductor in order to make the current flow path longer.

  FIG. 13 shows the loop antenna according to the eighth embodiment in which each conductor is formed such that the shape of the back pattern of each conductor is substantially equal to the shape of the surface pattern of each conductor in the loop antenna 41 shown in FIG. It is a transmission perspective view showing the shape of the conductor of an antenna. 13, the components corresponding to the components of the loop antenna 41 shown in FIG. 10 are denoted by the same reference numerals.

  In the loop antenna 71 according to the eighth embodiment, the shape obtained by combining the first surface pattern 3a and the second surface pattern 4a and the shape obtained by combining the first back pattern 3b and the second back pattern 4b are formed. , All have an inverted S shape when viewed from the front side. That is, when viewed from a direction perpendicular to the surface of the substrate 2, slits are formed in the first back pattern 3b and the second back pattern 4b at positions overlapping the gaps 5-1 and 5-2. ing. In addition, the width of the slit may be equal to the width of the gaps 5-1 and 5-2, or may be different from the width of the gaps 5-1 and 5-2. The first surface pattern 3a is electrically connected to the first back pattern 3b on the right end side. On the other hand, the second surface pattern 4a is electrically connected to the second back pattern 4b on the left end side. The first surface pattern 3a is not connected to the first back pattern 3b on the left end side of the substrate 2. Similarly, the second surface pattern 4 a is not connected to the second back pattern 4 b on the right end side of the substrate 2. The first back pattern 3b and the second back pattern 4b overlap each other at a position where the first tip 3d and the second tip 4d face each other, and are formed so as to be capable of electrostatic coupling. I have.

Therefore, in the loop antenna 71, since the path through which the current flows becomes longer than in the loop antenna 41, the inductance _Lap increases, and the required capacitance _Cint can be further reduced. As a result, in the loop antenna 71, the width of the gaps 5-1 and 5-2 can be made wider, and the fluctuation of the frequency characteristic due to a manufacturing error can be further reduced.

  Further, the gap between the first conductor 3 and the second conductor 4 may not be parallel to either the longitudinal direction or the lateral direction of the substrate 2.

  FIG. 14 is a schematic perspective view of a loop antenna according to a ninth embodiment in which each conductor is formed such that a gap between two conductors extends along a diagonal direction of the substrate. 14, the components corresponding to the components of the loop antenna 11 shown in FIG. 8 are denoted by the same reference numerals.

In the loop antenna 81 according to the ninth embodiment, on the surface of the substrate 2, the first surface pattern 3a becomes narrower toward the left end of the substrate 2 except for the portion where the feeding point 6a is provided, and The first surface pattern 3a is formed such that the lower end approaches the upper end. Similarly, the width of the second surface pattern 4a becomes smaller as approaching the right end of the substrate 2 except for the portion where the feeding point 6b is provided, and the upper end of the second surface pattern 4a approaches the lower end. Is formed. Therefore, the gap 5-1 and the gap 5-2 are formed along the diagonal line of the substrate 2. However, in a substantially central portion of the substrate 2, a projection is formed on the lower side of the first surface pattern 3a, and a projection is formed on the upper side of the second surface pattern 4a. The feed points 6a and 6b are provided on the protrusions so as to face each other along the longitudinal direction of the substrate 2. Thereby, also in the loop antenna 81, the path through which the current flows becomes longer than the length of one circumference of the substrate 2 along the longitudinal direction of the substrate 2, and the inductance _Lap can be increased. For this reason, the loop antenna 81 can also suppress the required capacitance C _int , so that the widths of the gaps 5-1 and 5-2 can be widened, and fluctuations in frequency characteristics due to manufacturing errors can be suppressed.

  In the loop antenna according to each of the above embodiments, the two conductors may be formed so as to be in direct contact on the back side of the substrate. Alternatively, the two conductors may be formed as one conductor. In this case, since there is no portion that is electrostatically coupled on the back side of the substrate, the capacitance of the loop antenna decreases. The decrease in the capacitance is compensated by, for example, reducing the gap between the conductors on the front surface side of the substrate.

Further, in the loop antenna according to each of the above-described embodiments, when the width of each conductor or the feeder line corresponding to the path through which current flows varies due to a manufacturing error in a process such as etching, the inductance _Lap also varies. As a result, the resonance frequency f0 also changes. In particular, the smaller the width of the current flowing path, the greater the ratio of the width variation of the portion due to the manufacturing error of the loop antenna to the width of the portion, so the influence on the variation of the inductance L _ap is also large. Become. For example, in the loop antenna 11 shown in FIG. 8, the loop antenna 11 is opposed to the tip 4 d of the second conductor 4 with the gap 5-1 interposed therebetween, and is interposed between the gap 5-1 and the upper end of the loop antenna 11. The variation in the width of the connecting portion 3c of the first conductor 3 affects the variation in the inductance _Lap . Similarly, the connection of the second conductor 4 facing the tip 3d of the first conductor 3 across the gap 5-2 and between the gap 5-2 and the lower end of the loop antenna 11 The variation of the width of the portion 4c affects the variation of the inductance _Lap .

  If the resonance frequency f0 fluctuates, the performance of the loop antenna also deteriorates, and thus such fluctuation of the resonance frequency f0 is not preferable. For example, the fluctuation amount of the resonance frequency f0 is suppressed to be equal to or less than the antenna characteristic of the loop antenna according to each embodiment, for example, the permissible fluctuation amount of the communicable distance (for example, 10% to 20% of the communicable distance at the design frequency). Is preferred.

ここで、ΔL_apは、製造誤差によるインダクタンスL_apの変動量を表す。同様に、ΔC_int及びΔC_cpは、それぞれ、製造誤差による静電容量C_int、C_cpの変動量を表す。（２）式から明らかなように、共振周波数f0を一定に保つためには、インダクタンスL_apが増加する場合（すなわち、ΔL_ap＞０）には、静電容量C_intまたは静電容量C_cpの少なくとも一方が減少することが求められる（すなわち、ΔC_int＜０またはΔC_cp＜０）。逆に、インダクタンスL_apが減少する場合（すなわち、ΔL_ap＜０）には、静電容量C_intまたは静電容量C_cpの少なくとも一方が増加することが求められる（すなわち、ΔC_int＞０またはΔC_cp＞０）。 Here, referring to the equation (1), if L _ap (C _int + C _cp ) is constant, the resonance frequency f0 is also constant. In other words, so as to suppress the fluctuation of the resonance frequency f0 corresponding to the variation of the inductance L _ap due to manufacturing errors, the electrostatic capacitance C _int or C _cp may be variations. This is expressed by the following equation.

Here, ΔL _ap represents a variation amount of the inductance L _ap due to a manufacturing error. Similarly, ΔC _int and ΔC _cp represent the amounts of change in the capacitances C _int and C _cp due to manufacturing errors, respectively. (2) As apparent from the equation, in order to keep the resonance frequency f0 to a constant, the inductance L _{if ap} is increased (i.e., [Delta] L _ap> 0), the capacitance C _int or capacitance C _cp Is required to decrease (ie, ΔC _int <0 or ΔC _cp <0). Conversely, when the inductance L _ap decreases (ie, ΔL _ap <0), it is required that at least one of the capacitance C _{int and the} capacitance C _cp increase (ie, ΔC _int > 0 or ΔC _cp > 0).

Referring now again to FIG. 8, the connecting portion 3c which mainly affects the variation of the inductance L _ap, 4c is adjacent to the gap 5-1 and 5-2 to provide an electrostatic capacitance C _int. Therefore, if the width of the connection portions 3c, 4c changes, the width of the gaps 5-1 and 5-2 also changes.

FIGS. 15A and 15B are diagrams illustrating an example of a change in the width of each conductor and the width of the gap due to a manufacturing error in the loop antenna 11, respectively. As shown in FIG. 15 (a), when the etching is excessively performed, the actual conductors 3 ′, 4 ′, as shown by dotted lines, correspond to the sizes of the conductors 3, 4 determined by design values. 'Becomes smaller. Therefore, the width of the first conductor 3 ′ and the width of the second conductor 4 ′ on the path through which current flows are smaller than the width of the first conductor 3 and the width of the second conductor 4. Then, as the width of the first conductor 3 'and the width of the second conductor 4' on the path through which the current flows are reduced, the inductance _Lap mainly generated by these conductors is increased. That is, ΔL _ap > 0. On the other hand, the width of the gap 5-1 and the gap 5-2 increases as the size of the actual conductors 3 ′ and 4 ′ decreases. Therefore, the capacitance C _int mainly caused by these gaps decreases. That is, ΔC _int <0.

Further, as shown in FIG. 15 (b), if the etching is too small, the actual conductors 3 ″, 3 ″, The size of 4 "becomes larger. Therefore, the width of the first conductor 3 ″ and the width of the second conductor 4 ″ on the path through which current flows are wider than the width of the first conductor 3 and the width of the second conductor 4. As a result, the inductance L _ap mainly caused by these conductors is reduced. That is, ΔL _ap <0. On the other hand, as the size of the actual conductors 3 ″ and 4 ″ increases, the width of the gap 5-1 and the gap 5-2 decreases. Therefore, the capacitance C _int mainly caused by these gaps increases. That is, ΔC _int > 0.

  Also in the loop antenna according to another embodiment, if the width of the portion where the current of each conductor flows is reduced due to a manufacturing error, the width of the gap between the conductors that causes capacitance is increased, and conversely, the current of each conductor is reduced. When the width of the portion where the flow of the gas flows increases due to manufacturing errors, the width of the gap decreases.

As described above, in the loop antenna according to each of the above embodiments, the capacitance C _int decreases when the inductance L _ap increases due to a variation in the width of the conductor due to a manufacturing error, and conversely, when the inductance L _ap decreases, the capacitance decreases. The capacity C _int increases. Therefore, if the width of the gap and the width of the conductor are appropriately set, the expression (2) is satisfied, and it can be seen that the resonance frequency f0 is kept constant even if the width of the conductor varies due to a manufacturing error.

  Further, in order to reduce the variation of the resonance frequency f0 due to the manufacturing error, in the relation of the value of the right side of the equation (2) with respect to the change of the conductor width, when there is no manufacturing error, the value of the right side of the equation (2) It is preferable that the width of each conductor is set so as to be an extreme value. That is, whether the width of each conductor becomes narrow or wide due to a manufacturing error, the value on the right side of Expression (2) becomes smaller than the value on the right side of Expression (2) when there is no manufacturing error. (Or larger). Thereby, the change in the value on the right side of the equation (2) with respect to the change in the width of the conductor becomes gentle, so that the fluctuation of the resonance frequency f0 due to a manufacturing error is suppressed.

For example, in the loop antenna 11, since the width of the connection portions 3c and 4c is relatively narrow, the ratio of the width change amount due to a manufacturing error to the width is also large. Thus, the influence of variations in the width of and the connection portion 4c of the connection portion 3c has on the [Delta] L _ap relatively large. From this, by appropriately adjusting the ratio of the width of the connection portion 3c and the width of the connection portion 4c to the width of the gap 5-1 and the gap 5-2, the fluctuation of the resonance frequency f0 due to a manufacturing error is suppressed. .

FIG. 16 is an electromagnetic field diagram showing an example of the relationship between the manufacturing error and the resonance frequency f0 of the loop antenna 11 when the fluctuation of the resonance frequency f0 due to the fluctuation of the inductance _Lap due to the manufacturing error is insufficient. FIG. 9 is a diagram showing a result of muting. In this simulation, the relative dielectric constant εr of the substrate 2 was set to 3.2 and the dielectric loss tangent tanδ of the substrate 2 was set to 0.001. The length of the substrate 2 in the longitudinal direction was 31 mm, the length in the lateral direction was 7 mm, and the thickness of the substrate 2 was 1.2 mm. The width G of the gap 5-1 and the gap 5-2 was set to 1.0 mm.

Further, the conductivity of the first conductor 3 and the second conductor 4 was set to 5.8 × 10 ⁷ (S / m). The width DW1 of the tip 3d of the first conductor 3 and the tip 4d of the second conductor 4 along the transverse direction of the substrate 2 is 4.4 mm, and the first conductor along the transverse direction of the substrate 2 is 4.4 mm. The width DW2 of the connecting portion 3c of No. 3 and the connecting portion 4c of the second conductor 4 was 1.6 mm. That is, G / DW2 = 0.625. Further, the width DL1 of the tip 3d of the first conductor 3 and the tip 4d of the second conductor 4 along the longitudinal direction of the substrate 2 was set to 11.5 mm. The length of the region where the integrated circuit 8 is provided along the longitudinal direction of the substrate 2 and the length of the region along the lateral direction of the substrate 2 were each 5 mm. The first conductor 3 and the second conductor 4 overlap each other on the back side of the substrate 2 within a range of 5.1 mm along the longitudinal direction of the substrate 2 and within 7 mm along the lateral direction of the substrate 2. I made it.

  In FIG. 16, the horizontal axis represents frequency, and the vertical axis represents communicable distance. Graph 1600 represents the frequency characteristics of loop antenna 11 when there is no manufacturing error. In addition, the graph 1610 shows the loop antenna 11 when the first conductor 3 and the second conductor 4 each become smaller by 0.05 mm along the outer circumference as shown in FIG. Indicates frequency characteristics. That is, in this example, DW2 = 1.5 mm and G = 1.1 mm. On the other hand, the graph 1620 shows the loop antenna 11 when the first conductor 3 and the second conductor 4 each become larger by 0.05 mm along the outer circumference as shown in FIG. Indicates frequency characteristics. That is, in this example, DW2 = 1.7 mm and G = 0.9 mm.

  As shown in the graphs 1600 to 1620, the frequency at which the communicable distance becomes the longest, that is, the resonance frequency f0 varies due to the variation in the size of each part of the first conductor 3 and the second conductor 4. I understand.

FIG. 17 shows an electromagnetic field simulation result showing an example of the relationship between the manufacturing error and the resonance frequency f0 of the loop antenna 11 when the fluctuation of the resonance frequency f0 due to the fluctuation of the inductance _Lap due to the manufacturing error is appropriately suppressed. FIG. In this simulation, the width G of the gap 5-1 and the gap 5-2 was set to 0.3 mm. The width DW1 of the tip 3d of the first conductor 3 and the tip 4d of the second conductor 4 along the transverse direction of the substrate 2 is set to 4.2 mm, and the first conductor along the transverse direction of the board 2 is set to 4.2 mm. The width DW2 of the connecting portion 3c of No. 3 and the connecting portion 4c of the second conductor 4 was 2.5 mm. That is, G / DW2 = 0.12. Further, the tip 3d of the first conductor 3 and the tip of the second conductor 4 along the longitudinal direction of the substrate 2 so that a resonance frequency substantially the same as the resonance frequency in the electromagnetic field simulation shown in FIG. The width DL1 of 4d was set to 10.65 mm. In addition, the size and physical characteristics of the substrate 2 were the same as those used in the electromagnetic field simulation shown in FIG.

  In FIG. 17, the horizontal axis represents frequency, and the vertical axis represents communicable distance. The graph 1700 shows the frequency characteristics of the loop antenna 11 when there is no manufacturing error. In addition, as shown in FIG. 15A, the graph 1710 shows the loop antenna 11 when the first conductor 3 and the second conductor 4 each become smaller by 0.05 mm along the outer circumference. Indicates frequency characteristics. That is, in this example, DW2 = 2.4 mm and G = 0.4 mm. On the other hand, the graph 1720 shows the loop antenna 11 when the first conductor 3 and the second conductor 4 each become larger by 0.05 mm along the outer circumference as shown in FIG. Indicates frequency characteristics. That is, in this example, DW2 = 2.6 mm and G = 0.1 mm.

  As shown in the graphs 1700 to 1720, even when the size of each part of the first conductor 3 and the second conductor 4 fluctuates, the frequency at which the communicable distance becomes the longest, that is, the resonance frequency f0 hardly fluctuates. You can see that. In this example, the resonance frequency f0 in the case where there is no manufacturing error shown in the graph 1700 is equal to the resonance frequency in the case where the width of each conductor is increased or reduced due to the manufacturing error as shown in the graphs 1710 and 1720. Higher than frequency f0. That is, it is understood that the width of each conductor is set so that the value on the right side of the equation (2) becomes an extreme value when there is no manufacturing error.

Note that, as in the loop antenna 41 shown in FIG. 10, the portion where the width of each conductor is the narrowest on the path through which current flows may be a portion sandwiched between the tip of one gap and the other gap. . In such a loop antenna, by appropriately adjusting the ratio of the width of the gap and the width of each conductor between the tip of one gap and the portion sandwiched by the other gap, as described above, due to a manufacturing error, The fluctuation of the resonance frequency f0 due to the fluctuation of the inductance _Lap is suppressed.

FIG. 18 is a diagram showing dimensions of each part of the loop antenna 41 designed to appropriately suppress a change in the resonance frequency f0 due to a change in the inductance _Lap due to a manufacturing error. In this simulation, the relative dielectric constant εr of the substrate 2 was set to 3.2 and the dielectric loss tangent tanδ of the substrate 2 was set to 0.001. The length of the substrate 2 in the longitudinal direction was 31 mm, the length in the lateral direction was 7 mm, and the thickness of the substrate 2 was 1.2 mm. The width G of the gap 5-1 and the gap 5-2 was set to 0.45 mm.

Further, the conductivity of the first conductor 3 and the second conductor 4 was set to 5.8 × 10 ⁷ (S / m). The width of the folded portion of the tip 3d of the first conductor 3 and the tip 4d of the second conductor 4 turned toward the integrated circuit 8 along the width direction of the substrate 2 was 1.40 mm. . In addition, the width of the portion of the front end 3d and the front end 4d excluding the folded portion along the lateral direction of the substrate 2 was set to 2.35 mm. Further, the length of the tip 3d and the tip 4d along the longitudinal direction of the substrate 2 was set to 9.00 mm. The width DW3 of the connection between the folded portion of the tip 3d and the tip 4d and another portion, that is, the portion between the tip of the gap 5-1 and the gap 5-2, or the tip of the gap 5-2 And the width of the portion sandwiched by the gap 5-1 was 0.20 mm. That is, G / DW3 = 2.25.

  The length of the connecting portion 3c of the first conductor 3 and the connecting portion 4c of the second conductor 4 along the longitudinal direction of the substrate 2 was set to 18 mm. The length of the region where the integrated circuit 8 is provided along the longitudinal direction of the substrate 2 and the length of the region along the lateral direction of the substrate 2 were each 5 mm. The first conductor 3 and the second conductor 4 overlap each other on the back side of the substrate 2 within a range of 5.1 mm along the longitudinal direction of the substrate 2 and within 7 mm along the lateral direction of the substrate 2. I made it. The width of the power supply line 9 was set to 0.26 mm.

19, in the case where designed to be adequately suppress variations in the resonance frequency f0 due to the variation of the inductance L _ap due to manufacturing errors, electromagnetic field showing an example of the relationship between a manufacturing error and the resonance frequency f0 of the loop antenna 41 It is a figure showing a simulation result.

  In FIG. 19, the horizontal axis represents frequency, and the vertical axis represents communicable distance. The graph 1900 shows the frequency characteristics of the loop antenna 41 when there is no manufacturing error. The graph 1910 shows the frequency characteristics of the loop antenna 41 when each of the first conductor 3 and the second conductor 4 is reduced by 0.05 mm along the outer circumference. That is, in this example, DW3 = 0.1 mm and G = 0.55 mm. On the other hand, a graph 1920 represents the frequency characteristics of the loop antenna 11 when each of the first conductor 3 and the second conductor 4 becomes larger by 0.05 mm along the outer circumference. That is, in this example, DW3 = 0.3 mm and G = 0.35 mm.

  As shown in the graphs 1900 to 1920, even when the size of each part of the first conductor 3 and the second conductor 4 changes, the frequency at which the communicable distance becomes the longest, that is, the resonance frequency f0 hardly changes. You can see that. Also in this example, the resonance frequency f0 in the case where there is no manufacturing error shown in the graph 1900 is equal to the resonance frequency in the case where the width of each conductor is increased or reduced due to the manufacturing error as shown in the graphs 1910 and 1920. Higher than frequency f0. That is, it is understood that the width of each conductor is set so that the value on the right side of the equation (2) becomes an extreme value when there is no manufacturing error.

Referring again to the equation (2), in order to suppress the fluctuation of the resonance frequency f0 due to the fluctuation of the inductance L _ap due to the manufacturing error, the capacitance C _cp is changed so as to cancel the fluctuation of the inductance L _ap. It turns out that you may do it. Alternatively, in order to suppress the variation of the resonance frequency f0 due to variations in the electrostatic capacitance C _cp, so as to offset the variation of the capacitance C _cp, inductance L _ap may vary.

FIG. 20 is a schematic side view near the integrated circuit 8 in the loop antenna 11 according to the second embodiment. The capacitance C _cp includes a component C _pad formed at a gap between the integrated circuit 8 and a mounting pattern 9 a for connecting to the integrated circuit 8, which is provided at a tip end of a power supply line connected to each conductor. The component C _pad varies depending on the area of the attachment pattern 9 a provided at the tip of the power supply line 9 and the width of the gap between the attachment pattern 9 a and the integrated circuit 8. Since the mounting pattern 9a is formed as a pattern on the substrate 2, for example, like the conductors, the area of the mounting pattern 9a fluctuates due to a manufacturing error in a process such as etching, like the conductors. That is, when the etching is performed excessively, the area of the mounting pattern 9a is reduced as the width of each conductor is reduced. As a result, in the attachment pattern 9a, the area of the portion facing the integrated circuit 8 also decreases, and the component C _pad decreases. Conversely, if the etching is too small, the area of the mounting pattern 9a increases as does the width of each conductor. As a result, in the attachment pattern 9a, the area of the portion facing the integrated circuit 8 also increases, and the component C _pad increases.

Therefore, in the loop antenna according to each of the above-described embodiments, the capacitance C _pad decreases when the inductance L _ap increases due to a change in the width of the conductor due to a manufacturing error, and conversely, when the inductance L _ap decreases, the capacitance C _pad decreases. _pad increases. Therefore, if the width of each conductor and the size of the mounting pattern are appropriately adjusted, equation (2) is established, and the resonance frequency f0 can be kept constant even if the width of the conductor fluctuates due to a manufacturing error. I understand.

Note that (2) As apparent from the equation, the variation of the resonance frequency f0 due to the variation of the inductance L _ap is inhibited by both the variation of the C _Pad included in change and the electrostatic capacitance C _cp of the capacitance C _int You may. Therefore, by appropriately adjusting the width of each conductor, the width of the gap between the conductors, and the size of the mounting pattern, the fluctuation of the resonance frequency f0 due to the fluctuation of the inductance _Lap due to a manufacturing error is also suppressed.

  In the loop antenna according to each of the above embodiments, the integrated circuit that feeds each conductor may be located at a position other than the center of the substrate. For example, the integrated circuit may be located on the left or right side of the center along the longitudinal direction of the substrate. In this case, the length of each conductor along the longitudinal direction on the side where the power supply point is provided is also adjusted according to the position of the integrated circuit. Further, in the loop antenna according to each embodiment, each conductor may be formed so as to surround the substrate along the lateral direction of the substrate. Further, in the loop antenna according to each embodiment, the width of the portion where the conductor is provided on the surface of the substrate and the width of the portion where the conductor is provided on the back side of the substrate along the direction perpendicular to the direction in which each conductor surrounds the substrate. May be different.

  Further, when each conductor included in the loop antenna according to each of the above embodiments is supported by, for example, a case in which the loop antenna is housed, the substrate may be omitted.

  FIG. 21 is a block diagram of a wireless tag having a loop antenna according to any of the above-described embodiments or their modifications. In this example, the wireless tag 150 is a passive RFID tag, and includes a loop antenna 151, a drive voltage generator 152, a memory 153, and a controller 154. Among them, the drive voltage generation unit 152, the memory 153, and the control unit 154 are examples of a communication processing circuit that radiates or receives a wireless signal via the loop antenna 151, and for example, includes an integrated circuit illustrated in FIG. Corresponds to circuit 8. The drive voltage generator 152, the memory 153, and the controller 154 may be formed as different parts of one integrated circuit, or may be formed as different circuits from each other.

  The loop antenna 151 is a loop antenna according to any of the above-described embodiments or its modifications. The loop antenna 151 receives, for example, a radio wave on which an interrogation signal including a preamble is radiated from a reader / writer (not shown), converts the radio wave into an electric signal, and is connected to a feeding point. It is passed to the drive voltage generator 152 and the controller 154.

  The drive voltage generation unit 152 generates a voltage for driving the memory 153 and the control unit 154 from the electric signal received from the loop antenna 151 using, for example, a preamble portion included in the electric signal, and generates the voltage. Is supplied to the memory 153 and the control unit 154. Note that any of various elements that convert an electric signal into a voltage and that is used in a wireless tag can be used as the drive voltage generation unit 152.

  The memory 153 has a nonvolatile semiconductor memory circuit. The memory 153 holds an ID code for identifying the wireless tag 150 from another wireless tag.

  The control unit 154 demodulates the electric signal received from the loop antenna 151 and extracts the interrogation signal carried by the electric signal. Then, the control unit 154 generates a response signal according to the inquiry signal. At that time, the control unit 154 reads the ID code from the memory 153 and includes the ID code in the response signal. Then, control section 154 superimposes the response signal on an electric signal having a frequency radiated from loop antenna 151. Then, control unit 154 outputs the electric signal to loop antenna 151, and causes loop antenna 151 to radiate the electric signal as a radio wave.

  All examples and specific terms provided herein are intended for instructional purposes to assist the reader in understanding the invention and the concepts contributed by the inventors to promoting the art. Yes, and it is to be construed not to limit the structure of any examples herein, such specific examples and conditions, to showing the advantages and disadvantages of the invention. While embodiments of the present invention have been described in detail, it should be understood that various changes, substitutions and modifications can be made thereto without departing from the spirit and scope of the invention.

The following additional remarks are further disclosed with respect to the embodiment described above and its modifications.
(Appendix 1)
A first pattern having conductivity and provided along the first surface and having a first feeding point, and connected to the first pattern at a first end of the first surface; A first conductor having a second pattern provided so as to face the first pattern;
A third pattern having conductivity and provided on the first surface with a gap that generates capacitance between the first pattern and the first pattern and having a second feeding point; A second end of the first surface facing the first end is connected to the third pattern and overlaps the second pattern so as to be electrostatically coupled thereto or the second pattern A second conductor having a fourth pattern connected to the second conductor;
Has,
At least a portion of the first pattern is located closer to the second end than at least a portion of the third pattern, and a current from the first feed point to the second feed point The first feeding point and the second feeding point are provided such that at least a part of the first pattern is included in the path of the first pattern.
Loop antenna.
(Appendix 2)
The loop antenna according to claim 1, wherein the first feeding point is provided closer to the second end than the second feeding point.
(Appendix 3)
The first feeding point is provided on the at least one side of the first pattern on a side facing the at least part of the third pattern, and the second feeding point is provided on the first pattern. 3. The loop antenna according to supplementary note 2, wherein the loop antenna is provided on the at least one side of the third pattern on the side facing the at least part of the pattern.
(Appendix 4)
The first pattern further includes a protrusion extending from the at least one side of the first pattern toward the first end along the third pattern,
Supplementary note 3, wherein the third pattern further includes a protrusion extending from the at least one side of the third pattern toward the second end along the first pattern. The loop antenna described.
(Appendix 5)
The connection between the at least a part of the first pattern and the first end and the first feeding point, the at least a part of the first pattern from the side of the first pattern 5. The loop antenna according to appendix 3 or 4, wherein the first slit is formed in a direction toward an end of the loop antenna.
(Appendix 6)
In the first pattern, the first pattern extends in a direction intersecting a path of a current flowing through the first conductor 3 and the second conductor 4 between the first feeding point and the second feeding point. The loop antenna according to claim 3 or 4, wherein the slit is formed.
(Appendix 7)
The loop antenna according to claim 5, wherein a slit is formed in the second pattern and the fourth pattern at a position overlapping the gap when viewed from a direction perpendicular to the first surface.
(Appendix 8)
The first pattern is formed so that a first side of the first pattern facing the second end has a meandering shape, and the first end of the third pattern is formed. The third side such that a second side facing the portion has a meandering shape along the first side, and the gap is formed between the first side and the second side. 3. The loop antenna according to appendix 1 or 2, wherein the pattern is formed.
(Appendix 9)
A dielectric substrate having the first surface;
The loop antenna according to any one of Supplementary notes 1 to 8, wherein the second pattern and the fourth pattern are provided on a surface of the substrate facing the first surface.
(Appendix 10)
The width of the gap and the size of a portion of the first pattern and the third pattern, the size of which varies in accordance with the variation of the width of the gap, are determined by the variation in the size of the portion. 10. The loop antenna according to any one of supplementary notes 1 to 9, wherein a change in a resonance frequency is set by a change in a width of the gap.
(Appendix 11)
The area of a conductive attachment pattern for attaching a circuit connected to the loop antenna to the loop antenna, and the size of the portion of the first pattern and the third pattern are smaller than the size of the portion. The loop antenna according to claim 10, wherein a change in a resonance frequency of the loop antenna due to the change is set to be suppressed by a change in the area of the attachment pattern according to a change in the size of the portion.
(Appendix 12)
A loop antenna having a first feeding point and a second feeding point;
A communication processing circuit that is connected to the loop antenna by a power supply line that supplies power to the first power supply point and the second power supply point, and radiates or receives a wireless signal via the loop antenna;
The loop antenna,
A first pattern having conductivity and provided along a first surface and having the first feeding point; and a first pattern at a first end of the first surface. A first conductor having a second pattern connected thereto and provided so as to face the first pattern;
A third pattern having conductivity and provided on the first surface with a gap that generates capacitance between the first pattern and the second pattern and having the second feeding point; A second end of the first surface facing the first end is connected to the third pattern, and overlaps with the second pattern so as to be electrostatically coupled, or A second conductor having a fourth pattern connected to the pattern;
Has,
At least a portion of the first pattern is located closer to the second end than at least a portion of the third pattern, and a current from the first feed point to the second feed point The first feeding point and the second feeding point are provided such that at least a part of the first pattern is included in the path of the first pattern.
Wireless tag.

1, 11, 21, 31, 41, 51, 61, 71, 81 Loop antenna 2 Substrate 3 First conductor 4 Second conductor 3a First surface pattern 4a Second surface pattern 3b First back pattern 4b 2nd back pattern 3c 1st connection part 4c 2nd connection part 3d 1st tip part 4d 2nd tip part 3e, 3g, 3h Projection part 4e, 4g, 4h Projection part 3f Slit 4f Slit 5-1 5-2 Gap 6a First feeding point 6b Second feeding point 7 Film layer 8 Integrated circuit 9 Feeding line 9a Mounting pattern 150 Wireless tag 151 Loop antenna 152 Driving voltage generator 153 Memory 154 Control unit

Claims (6)

A first pattern having conductivity and provided along the first surface and having a first feeding point, and connected to the first pattern at a first end of the first surface; A first conductor having a second pattern provided so as to face the first pattern;
A third pattern having conductivity and provided on the first surface with a gap that generates capacitance between the first pattern and the first pattern and having a second feeding point; A second end of the first surface facing the first end is connected to the third pattern and overlaps the second pattern so as to be electrostatically coupled thereto or the second pattern A second conductor having a fourth pattern connected to the second conductor;
Has,
At least a portion of the first pattern is located closer to the second end than at least a portion of the third pattern, and a current from the first feed point to the second feed point The first feeding point and the second feeding point are provided so that at least a part of the first pattern is included in the path of the first pattern , and the first feeding point is the second feeding point. Provided closer to the second end than the feed point ;
Loop antenna. The first feeding point is provided on the at least one side of the first pattern on a side facing the at least part of the third pattern, and the second feeding point is provided on the first pattern. 2. The loop antenna according to claim 1 , wherein the loop antenna is provided on the at least one side of the third pattern on a side facing the at least part of the pattern. 3. The first pattern further includes a protrusion extending from the at least one side of the first pattern toward the first end along the third pattern,
3. The third pattern, further comprising a protrusion extending from the at least a part of the side of the third pattern toward the second end along the first pattern. 4. A loop antenna according to any one of the above. The connection between the at least a part of the first pattern and the first end and the first feeding point, the at least a part of the first pattern from the side of the first pattern The loop antenna according to claim 2 , wherein the first slit is formed in a direction toward the end of the loop antenna. The first pattern is formed so that a first side of the first pattern facing the second end has a meandering shape, and the first end of the third pattern is formed. The third side such that a second side facing the portion has a meandering shape along the first side, and the gap is formed between the first side and the second side. The loop antenna according to claim 1, wherein the following pattern is formed. A loop antenna having a first feeding point and a second feeding point;
A communication processing circuit that is connected to the loop antenna with a power supply line that supplies power to the first power supply point and the second power supply point, and radiates or receives a radio signal via the loop antenna;
The loop antenna,
A first pattern having conductivity and provided along a first surface and having the first feeding point; and a first pattern at a first end of the first surface. A first conductor having a second pattern connected thereto and provided so as to face the first pattern;
A third pattern having conductivity and provided on the first surface with a gap that generates capacitance between the first pattern and the second pattern and having the second feeding point; A second end of the first surface facing the first end is connected to the third pattern, and overlaps with the second pattern so as to be electrostatically coupled thereto, or A second conductor having a fourth pattern connected to the pattern;
Has,
At least a portion of the first pattern is located closer to the second end than at least a portion of the third pattern, and a current from the first feed point to the second feed point The first feeding point and the second feeding point are provided so that at least a part of the first pattern is included in the path of the first pattern , and the first feeding point is the second feeding point. Provided closer to the second end than the feed point ;
Wireless tag.

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